"Zatara," bamboo backed osage bow, part 2 - rough limb tapering

As mentioned in the last post, the outside of the stave section from which the limb section was taken was in pretty bad shape. My hope was that by turning the back of the staves into the belly of the limbs, the problem areas would come off in tapering and tillering. Since this is going to be a backed bow, I can really treat these sections as lumber and go ahead and give them a rough taper before glue up. I'll refine the taper/tiller after it's all glued up and already starting to bend.

The limb thickness of the osage is currently a nominal half inch (just under), and I want to taper it out about 1/8" along the limb. I'll start the taper just outside where the handle section will get glued over the splice. The pieces are long enough that I can get a full 66-67" nock to nock length. Since the overall length is close to 69" and my handle is 9", I'll plan to taper 29" for each limb, which will give me a half inch margin on either side of the handle as a "safety zone" to eventually bring down when tillering.

The ideal way to taper this dimensional stock would be to use a planer, which would allow me to take 4 passes of 1/32" and call it a day. I don't have a planer, so I'm going to go to the bandsaw instead. When I first started building bows, I took a bow class in which we built bamboo backed ipe longbows by first tapering the stock by cutting it on the bandsaw using a .005" per inch pre-tapered piece of wood attached to the stock. On 29", I calculate that this makes closer to 5/32" than 1/8" (.145" total taper, to be exact), but in practice I have found that it is close enough to what I want that it works just fine. It generally means that most of the refining I do to the tiller happens in the inner limbs first.

This job is going to be a little trickier, as the stave originally had some good reflex to it. Since I'm orienting the grain in the the opposite direction, I'm actually fighting the wood a bit. Here is one of the future limbs next to my pre-tapered stock. One can see the amount of the reflex pretty clearly. In order to keep it in place for tapering on the bandsaw, I'm going to use my favorite secret weapon: blue painter's tape!

Here you can see the limb section taped to the pre-tapered stock. You'll also notice blue clamps in place. I use those to hold the limb in place against the stock so it is as flat against it as possible. The taping actually uses a technique I picked up from lutherie: One stretches the tape while applying it so that it exerts some clamping/pulling force. How much does it stretch? Not much, but enough to create some reasonable force on the two pieces, especially when applied in quantity as it is here. How much stretching is too much? If the tape snaps, you've gone too far. It's a nice self-correcting exercise.

 

Because the limb section is already at its maximum thickness near the handle, setting up the bandsaw fence is relatively easy: I just put the taped up piece next to the blade just outside of where I want the cut to stop, then slide the fence over until the stock is slightly snug against the blade and the teeth of the blade catch the tape when trying to pull it through. This lets me know that the blade will effectively stop cutting at that point -- plus there's that half inch "safety zone" I mentioned.

All the prep work for taping it in place took a considerable amount of time, but putting it through the bandsaw couldn't have gone smoother. Because of the direction of flex in the piece, as each part is cut and is freed from the tape, the section actually pulls away after the cut, which means that the taper is pretty consistent. Luck also appears to be on my side, as the bad sections of the piece have come just away in the tapering process. You can see the before and after in the photos below.

Limb 1: before

Limb 1: after

Limb 2: before

Limb 2: after